Updated 13:08

EU President Donald Tusk has said that Britain must resolve the issue of Ireland before talks begin on a post-Brexit trade deal. 

Tusk sent a letter out to the remaining 27 member states before an EU summit taking place this weekend. 

Meanwhile, a proposal from the Irish government is set to be discussed tomorrow at the summit which would ensure Northern Ireland could immediately rejoin the EU in the event of a united Ireland.

In Tusk's letter to the remaining member states he said "Before discussing EU-UK future, we must first sort out our past. This is the only possible approach to Brexit talks."

Before discussing EU-UK future, we must first sort out our past. This is the only possible approach to Brexit talks.https://t.co/D2qIqhvBtu

— Donald Tusk (@eucopresident) April 28, 2017

He continued by saying "Following the United Kingdom's notification of withdrawal from the European Union, we will meet on Saturday for the first time as the formal European Council of 27 to adopt guidelines for the upcoming Brexit negotiations. 

He said there is one element of the talks which has to be a priority "I am referring to the idea of a phased approach, which means that we will not discuss our future relations with the UK until we have achieved sufficient progress on the main issues relating to the UK's withdrawal from the EU.

"This is not only a matter of tactics, but , given the limited time frame we have to conclude the talks, it is the only possible approach. In other words, before discussing our future, we must first sort out our past."

Good Friday Agreement 

Tusk made it clear that the issue of Ireland needs to be resolved before trade talks can ensue "Finally, in order to protect the peace and reconciliation process described by the Good Friday Agreement, we should aim to avoid a hard border between the Republic of Ireland and Northern Ireland. 

"Only once we collectively determine in the European Council that sufficient progress has been made on all these issues, will we be in a position to hold preparatory talks on the future relationship with the UK."

He finished by saying "I would like us to unite around this key principle during the upcoming summit, so that it is clear that progress on people, money and Ireland must come first. And we have to be ready to defend this logic during the upcoming negotiations."

Adams' response 

The Sinn Fein president has welcomed the suggestion by the President of the European Council.

It's being taken as a sign that tomorrow's EU summit will result in a deal to let Northern Ireland rejoin the EU straight away in a United Ireland.